The long-term objective of the project is the development of a small, low cost hybrid positron camera for use in oncologic clinical and research projects. The camera should possess the capability to image objects less than 20 cm in diameter in a three-dimensional tomographic mode and two target areas of 12.5 x 18 cm in larger objects with a stationary, multi- view planar mode. The technical aim of the project is to produce the preliminary system test platform which will have a highly abridged version of the hybrid positron camera. The health application aim of the project is to provide an alternative method of positron imaging to that currently available for detecting primary, metastatic and recurrent tumors in the range of two to four mm, for determining, at an earlier time, response of cancer to treatment, for measuring the functional metabolic characteristics of tumors and for evaluating small animal tumor models. An important specific health application of the project involves utilizing the camera to detect and monitor treatment response of breast tumors with superior resolution and sensitivity. The financial aim is to produce informative oncologic images with a small positron camera costing one-fourth the price of commercial PET. The camera will consist of a detector ring 25 cm in diameter with a 20 x 12.5 cm field-of-view in tomographic mode. The detector ring can be separated into four quadrants which can be offset from each other for planar imaging. The hybrid detector ring will be designed using a quadrant-PMT-sharing scheme with crystal blocks to improve image resolution while keeping the cost low. The initial system test platform will be built to test the imaging concept on phantoms, to measure the physical characteristics of the full camera and to perform preliminary clinical and animal experiments in the future. In support of the system test platform, electronics, software and phantoms which are suitable for control, data acquisition and simulation of operating conditions will be developed. Experiments will also be conducted for the purpose of enhancing and quantitating the two- dimensional projection images acquired by the camera in the multi-view planar mode. Quantitation methods which will be investigated include a combination of background subtraction, two-dimensional Fourier-domain filtering, limited-angle back-projection, multi-angle projection averaging, and curve-surface fitting.